Process for producing oxygen by fractionation of air at low temperatures in small installations



Aug. 16, 1966 R. BECKER 3,266,259

PROCESS FOR PRODUCING OXYGEN BY FRACTIONATION OF AIR AT LOW TEMPERATURES IN SMALL INSTALLATIONS Filed Jan. 24, 1963 United States Patent 3,266,259 PROCESS FOR PRODUCING OXYGEN BY FRAC- TIONATION OF AIR AT LOW TEMPERATURES IN SMALL INSTALLATIONS Rudolf Becker, Munich-Solln, Germany, assignor to Linde Aktiengeseiischaft Filed Jan. 24, 1963, Ser. No. 253,591 Claims priority, applicatiozgn (llermany, Jan. 26, 1962,

3 Claims. (Cl. 62--14) This invention relates to a method and apparatus for obtaining oxygen by fractionation of air at low temperatures, particularly where the oxygen demand is relatively low, and where it is desirable for the installation to be physically small, and relatively free of maintenance difficulties.

It has heretofore been necessary in small oxygen producing plants to employ high compression with low temperature drying and alkali absorption of carbon dioxide. An oxygen compressor was also sometimes required. Such installations, however, occupied much space, and required much servicing.

The principal object of this invention, therefore, is to provide a novel process and apparatus which is small in size and relatively maintenance-free for the production of oxygen in relatively modest quantities.

Upon further study of the specification and appended claims, other objects and advantages of this invention will become apparent.

. The present invention comprises a system in which the water vapor and carbon dioxide of the air are deposited in regenerators, said deposits being ultimately vaporized by scavenging gases. A portion of the highly cooled and purified air from the regenerator is reheated and after being expanded while preferably doing external work, is passed in part to the rectification column. The other portion of the cooled and cleaned gas from the regenerator after passing through heat exchange tubes in the bottom of the column and then through an expansion valve, is introduced into the upper part of the column. The process of this invention is also particularly characterized by the fact that only from one-tent-h to one-third, more preferably one-seventh of one fourth, of the oxygen content of the air supplied to the system is withdrawn from the bottom of the column in liquid form, pressurized by a pump, and vaporized by heat from any convenient source, while the other portion of the air is used as scavenging gas in at least one of the regenerators.

The attached drawing is schematic flo-wsheet of a preferred embodiment of this invention.

The portion of the air that is used as scavenging gas is also advantageously passed through a heat exchanger in countercurrent relation to that portion of the air which is being conducted to the heat exchange tubes in the bottom of the rectifier so as to avoid any loss of heat during reversal of the regenerators.

The apparatus of this invention comprises at least two regenerators which are interchangeable for use with either compressed air or cavenging gas. Each regenerator has a built-in heating coil in its cooler part. The apparatus also comprises a single rectification column which has its sump or bottom provided with a heating means, such as tubes, and an oxygen-outlet pipe connection. The heating means has one end thereof connected to the air outlet from the cooler part of the regenerator and the other end thereof connected through an expansion valve with the upper portion of the rectification column. Also included is an expansion turbine for the air which has been highly cooled in the regenerator and then somewhat reheated. Additionally there may be provided a pressure pump and a heater for vaporizing the liquefied oxygen under pressure, the heater being supplied with heat from any source, such as by product process steam or hot water.

A regulating valve can be used advantageously for admitting only a portion of the expanded air to the column and for diverting preferably the greater portion of it through a branch conduit to the regenerators for use as cooling and scavenging fluid.

There is also a heat exchanger in counter-current relation between the air that is to be used as scavenging fluid for the regenerators and the air that is to be passed through the heating means in the sump of the column.

The compression of the air to 6-8 atmospheres is preferably accomplished with oil-free machines such as screw compressors or piston compressors with Teflon rings. The energy consumption of such an apparatus is definitely greater than normal and amounts to about 2.5 kilowatts per hour per Nm. of oxygen produced, as against about 1.1 kw./h. per Nm. of oxygen for normal plants. Nevertheless the apparatus is overall definitely more economical, mainly because of lower maintenance costs.

The preferred process of this invention comprises the steps of:

(l) compressing raw air to about 6-8 atmospheres;

(2) passing the compressed air through a regenerator to cool it and to deposit water and carbon dioxide impurities inside the regenerator;

(3) dividing the resultant cooled and cleaned air into two portions;

(4) passing the first portion of about -80% of the total cooled and cleaned air through a regenerator whereby the air is reheated;

(5) expanding said reheated air,

doing external work;

(6) dividing the resultant expanded first portion into two parts:

6(a) passing the first part (about 15-45% more preferably about 20-32% of the first portion) into a rectification column;

6(b) passing the second part of the: first portion to a heat exchanger;

(7) passing the second portion of about 15-20% of the total cooled and cleaned air through the heat exchanger of step 6(b) in indirect heat exchange retionship with the second part of the first portion whereby the second portion is cooled;

(8) passing the cooled second portion through the bottom of the rectification column and in indirect heat exchange relationship with the contents of said column, whereby the second portion acts as a heating medium for rectification and is thereby liquefied;

(9) expanding the liquefied second portion;

(10) passing the resultant expanded second portion into the upper zone of the rectification column;

(11) rectifying the expanded second portion step (10) and the first part of the first portion step 6(a) in said rectification column to produce a bottoms fraction of oxygen and an overhead fraction of air partially depleted of oxygen;

(12) passing the overhead to the heat exchanger of step 6(b) and mixing it with said second part of the first portion, and in indirect heat exchange relationship with said second portion;

(13) passing the resultant heated gaseous mixture of the overhead and second part of the first portion, as scavenging gas, to a regenerator containing deposited H 0 and CO therein, whereby the scavenging gas removes said impurities from the regenerator;

(l4) compressing the pure oxygen bottoms fraction from the rectification column step (11), and

(15) heating the resultant compressed liquid oxygen to vaporize same.

more preferably while Without further elaboration, it is believed that the preceding description will enable one skilled in the art to practice this invention to its fullest extent. For purposes of even further illustration, however, two preferred specific embodiments will now be described with reference to the attached drawing, it being understood that these embodiments are merely exemplary in nature, and do not function to restrict the invention as set forth in the other portion of the specification and appended claims.

EXAMPLE 1 1000 Nm. /h. air are delivered by conduit 1 to the compressor 2 for compression to about 8 atmospheres The compressed air is delivered by conduit 3 through control valve 4a to one of the two regenerators 5 and 6, and in this case the regenerator 5. In this regenerator the air is highly cooled and freed from water vapor and carbon dioxide. The cooled and purified air, after passing through the valve 7a, enters the conduit 8. A considerable portion of it, 810 Nm. /h. is branched from conduit 8 through conduit 9, through the coils 10 to conduit 11 and under a pressure of 5.6 atm. and at 117 K. to the expansion turbine 12. The expanded air is then passed through conduit 13 and regulating valve 13a diverting about 160 Nm. of the expanded air at 1.3 atm. and 84 K. into the single rectification column 14, while the remaining 650 Nm. /h. is returned through conduit 13b and heat exchanger 15 to conduit 21 for use as scavenging gas for one of the regenerators.

Meanwhile, back at the branch, the remaining 160 Nm. /h of the cleaned and cooled air passes at 100 K. in conduit 8 through heat exchanger 15, and then at 91 K. through conduit 16 and through the heating coil 17 in the sump of the column 14. The air that is liquefied in this coil is then passed at 97 K. through pipe 18 to the expansion valve 19 for delivery to the upper part of the column 14. From the head of this column, 290 Nm. /h. of air which has had some of its oxygen removed (about 30 Nm. /h.) is passed through conduit 20 to the heat exchanger 15, where it mixes with the above-mentioned 650 NmF/h. of expanded air from conduit 13b for passage through the heat exchanger, conduit 21, and then through the valve element 7 1; into one of the regenerators, for example regenerator 6, and from there through valve 4b and conduit 22 for escape to the atmosphere.

From the sump of column 14, the pipe 23 delivers 30 Nm. /h. of liquid oxygen to the pressure pump 24. The pressurized liquid oxygen is delivered by pipe 25 to a heater 26, which can be operated with warm water as the heating medium. Here the liquid oxygen is vaporized and delivered through conduit 27 as gaseous oxygen. For every 1000 Nm. h. of air that was originally introduced into the system, 30 Nm. h. of oxygen is thus taken out, which constitutes one-seventh of the total amount of oxygen in the air.

EXAMPLE 2 According to another embodiment, out of a total of 800 Nm. /h. of expanded air from the turbine 12, about 250 Nm. /h. are delivered through conduit 13 to the column 14 while 550 Nm. /h. are sent back for use as scavenging gas. The remainder of the highly cooled and cleaned air (170 Nm. /h.) is passed through the heat exchanger 15, heater 17 and pipe 18 to the expansion valve 19 and from there is delivered to the upper part of the rectifier.

370 Nm. /h. of air which has been partly stripped of its oxygen is then delivered by conduit 20 to the heat exchanger where it is combined with the 550 NmS /h. of expanded air and is returned for use as scavenging gas. During the same time, Nm. /h. of oxygen under pressure is removed from the sump. This amounts to slightly less than one-fourth of the oxygen in the original air.

This unusually simple installation is largely automatic in its operation and is exceptionally suitable for the proi duction of bottled oxygen or for supplying a factory with oxygen. It is also possible, by omitting the heater 26, to obtain liquid oxygen.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention, and without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. Consequently, such changes and modifications are properly, equitably, and intended to be, Within the full range of equivalence of the following claims.

What is claimed is:

1. A process for the low temperature separation of oxygen from air, which process comprises:

(1) compressing raw air to about 6-8 atmospheres;

(2) passing the compressed air through a regenerator to cool it and to deposit water and carbon dioxide impurities inside the regenerator;

(3) dividing the resultant cooled and cleaned air into two portions;

(4) passing the first portion of about -80% of the total cooled and cleaned air through coils embedded in the regenerators whereby the air is reheated;

(5) expanding said reheated air while doing external work;

(6) dividing the resultant expanded first portion into two parts;

6(a) passing the first part of about 1545% of the first portion into a rectification column; 6(b) passing the second part of the first portion to a mixing point;

(7) passing the cooled second portion through the bottom of the rectification column and in indirect heat exchange relationship with the contents of said column, whereby the second portions acts as a heating medium for rectification and is thereby liquefied;

(8) expanding the liquefied second portion;

(9) passing the resultant expanded second portion into the upper zone of the rectification column;

(10) rectifying the expanded second portion step (9) and the first part of the first portion step 6(a) in said rectification column to produce a bottoms fraction of oxygen and an overhead fraction of air partially depleted of oxygen;

(11) withdrawing liquid oxygen from the bottom of said rectification column only in a quantity of one tenth to one-third of the oxygen content of the compressed .raw air step (1) (12) passing the overhead to the mixing point of step 6(b) and mixing it with the second part of the first portion; and

(13) passing the resultant gaseous mixture of the overhead and second part of the first portion, as scavenging gas, to a regenerator containing deposited H 0 and CO therein, whereby the scavenging gas removes said impurities from the regenerator.

2. A process for the low temperature separation of oxygen from air, which process comprises:

(1) compressing raw air to about 6-8 atmospheres;

(2) passing the compressed air through a regenerator interchangeable with a scavenging gas to cool the and and to deposit water and carbon dioxide impurities inside the regenerator;

(3) dividing the resultant cooled two portions;

(4) passing the first portion of about 8580% of the total cooled and cleaned air through coils embedded in said regenerators whereby the air is reheated;

(5) expanding said reheated air While doing external work;

(6) dividing the resultant expanded first portion into two parts;

6(a) passing the first part of about 15-45% of the first portion into a rectification column;

and cleaned air into 6(b) passing the second part of the first portion to a heat exchanger;

(7) passing the second portion of about 15-20% of the total cooled and cleaned air through the heat exchanger of step (6b) in indirect heat exchange relationship with the second part of the first portion whereby the second portion is cooled;

(8) passing the cooled second portion through the bottom of the rectification column and in indirect heat exchange relationship with the contents of said column, whereby the second portion acts as a heating medium for rectification and is thereby liquefied;

(9) expanding the liquefied second portion;

(10) passing the resultant expanded second portion into the upper zone of the rectification column;

(11) rectifying the expanded second portion step (10) and the first part of the first portion step 6(a) in said rectification column to produce a bottoms fraction of oxygen and an overhead fraction of air partially depleted of oxygen;

(12) withdrawing liquid oxygen from the bottom of said rectification column only in a quantity of onetenth to one-third of the oxygen content of the compressed raW air step (1) (13) passing the overhead to the heat exchanger of step 6(b) and mixing it with said second part of the first portion, and in indirect heat exchange relationship With said second portion; and

(14) passing the resultant heated gaseous mixture of the overhead and second part of the first portion, as scavenging gas, to a regenerator containing deposited H20 and CO2 therein, whereby the scavenging gas References Cited by the Examiner UNITED STATES PATENTS Schilling 62-14 Pool 62-13 Rice 62-14 Becker 6238 First 6214 Schilling 62-41 Yendall 62-13 NORMAN YUDKOFF, Primary Examiner. 

1. A PROCESS FOR THE LOW TEMPERATURE SEPARATION OF OXYGEN FROM AIR, WHICH PROCESS COMPRISES: (1) COMPRESSING RAW AIR TO ABOUT 6-8 ATMOSPHERES; (2) PASSING THE COMPRESSED AIR THROUGH A REGENERATOR TO COOL IT AND TO DEPOSITE WATER AND CARBON DIOXIDE IMPURITIES INSIDE THE GENERATOR; (3) DIVIDING THE RESULTANT COOLED AND CLEANED AIR INTO TWO PORTIONS; (4) PASSING THE FIRST PORTION OF ABOUT 85-80% OF THE TOTAL COOLED AND CLEANED AIR THROUGH COILS EMBEDDED IN THE REGENERATORS WHEREBY THE AIR IS REHEATED; (5) EXPANDING SAID REHEATED AIR WHILE DOING EXTERNAL WORK; (6) DIVIDING THE RESULTANT EXPANDED FIRST PORTION INTO TWO PARTS; 6(A) PASSING THE FIRST PART OF ABOUT 15-45% OF THE FIRST PORTION INTO A RECTIFICATION COLUMN; 6(B) PASSING THE SECOND PART OF THE FIRST PORTION TO A MIXING POINT; (7) PASSING THE COOLED SECOND PORTION THROUGH THE BOTTOM OF THE RECTIFICATION COLUMN AND IN INDIRECT HEAT EXCHANGE RELATIONSHIP WITH THE CONTENTS OF SAID COLUMN, WHEREBY THE SECOND PORTIONS ACTS AS A HEATING MEDIUM FOR RECTIFICATION AND IS THEREBY LIQUEFIED; (8) EXPANDING THE LIQUEFIED SECOND PORTION; (9) PASSING THE RESULTANT EXPANDED SECOND PORTION INTO THE UPPER ZONE OF THE RECTIFICATION COLUMN; (10) RECTIFYING THE EXPANDED SECOND PORTION STEP (9) AND THE FIRST PART OF THE FIRST PORTION STEP 6(A) IN SAID RECTIFICATION COLUMN TO PRODUCE A BOTTOMS FRACTION OF OXYGEN AND AN OVERHEAD FRACTION OF AIR PARTIALLY DEPLETED OF OXYGEN; (11) WITHDRAWING LIQUID OXYGEN FROM THE BOTTOM OF SAID RECTIFICATION COLUMN ONLY IN A QUANTITY OF ONETENTH TO ONE-THIRD OF THE OXYGEN CONTENT OF THE COMPRESSED RAW AIR STEP (1); (12) PASSING THE OVERHEAD TO THE MIXING POINT OF STEP 6(B) AND MIXING IT WITH THE SECOND PART OF THE FIRST PORTION; AND (13) PASSING THE RESULTANT GASEOUS MIXTURE OF THE OVERHEAD AND SECOND PART OF THE FIRST PORTION, AS SCAVENGING GAS, TO A REGENERATOR CONTAINING DEPOSITED H2O AND C2O THEREIN, WHEREIN THE SCAVENGING GAS REMOVES SAID IMPURITIES FROM THE GENERATOR. 